The present invention relates generally to a fatigue alarm system and method for an automotive vehicle driver for detecting fatigue accumulated during vehicle driving and cautioning the driver when the driver's accumulated fatigue reaches a predetermined level. More particularly, the invention relates to a fatigue alarm system for detecting accumulated driver fatigue by measuring the period of time for which the driver has been driving.
It is well known that it is recommendable to take a rest after every two or two and a half hours of driving in order to refresh oneself and recover from driving fatigue. It is especially necessary for the driver to take a rest after driving for a relatively long time.
Various alarm devices for producing rest suggestions have been developed and proposed. For example, published Japanese Utility Model (Jikko Sho) No. 48-15104 shows an alarm device which is associated with a tachograph to produce an alarm at a given time. On the other hand, unexamined Japanese Utility Model (Jikkai Sho) No. 51-156878 shows a device for displaying a required resting period of time depending on the preceding driving period.
Since the foregoing devices are adapted to deliver messages to the driver at certain fixed times, the alarm timing does not always correspond to the driver's fatigue. For example, if the driver takes a rest before the given time or if driving conditions vary significantly, the fixed alarm timing will not correspond to the driver's fatigue.
To ameliorate the above-mentioned defect, Published Japanese Utility Model (Jikkai Sho) No. 52-13232 shows another alarm device which counts the pulses of a clock signal in order to detect the timing at which to give the alarm. In this device, the timing is detected by analog processing of the clock signal.
In addition, Published Japanese Utility Model (Jikkai Sho) No. 51-156878 discloses an alarm device adapted to detect accumulation of fatigue of an automotive vehicle driver and to set an alarm clock to produce an alarm. The detection of accumulation of fatigue is based on selected driving conditions of the vehicle and the period of time for which the detected driving conditions are maintained. Fatigue data obtained on the basis of the driving conditions and the time is integrated to derive a correction or update value for the preset time, which is to be compared with the actual driving time. The alarm device is activated when the driving time reaches the updated time.
In this case, in order to measure the total driver fatigue accurately, it is necessary to reduce the fatigue total value in accordance with the rests taken by the driver in order to reflect the practical fatigue condition of the driver. On the other hand, even when the vehicle is at rest and preselected rest parameters, such as a vehicle speed of zero and application of a parking brake, are satisfied, the driver is not necessarily resting. Vehicle conditions similar to those extant during driver restperiods may occur even while driving. For example, when the vehicle comes to rest at a stop signal, the driver is apt to apply the parking brake. If application of the parking brake and zero vehicle speed are taken as parameters indicating that the driver is resting, then such cases as described above may also be regarded as resting time.
This would degrade the accuracy of detection of the driver fatigue. Therefore, in order to monitor the driver's fatigue accurately, it is necessary to distinguish whether or not vehicle rest corresponds to the driver's rest.